The importance of engine capacity in cars

Whether it's a lively small car or a powerful SUV – the displacement reveals a lot about the character and handling of a car. But what does displacement actually mean exactly? And why does it affect performance, fuel consumption and even the driving experience? In this guide, you will learn in an easy-to-understand way why engine capacity is one of the most exciting key figures when buying a car - and what you should pay attention to.

⏰ Summary

• Definition of displacement
• Calculating the displacement is complicated
• Short-stroke and long-stroke – what are they?
• More displacement = (almost) more power
• Be careful with displacement increases

If you are interested in a new car, here are a few offers:

 

What is Displacement – The Definition

Displacement refers to the volume that the pistons in the engine displace when moving up and down. It is given in cubic centimeters (cm³) or liters. A larger displacement allows for more power, but usually also leads to higher fuel consumption.

An engine has several cylinders and a piston can be found in each of these cylinders. This piston moves up and down with each explosion of the fuel-air mixture. The displacement is then the total volume of all cylinders.

Here is a pictorial explanation of this technical term, so that you can better imagine what a displacement is.

Imagine two people:

• A well-trained sprinter with huge lung volume
• An amateur jogger with smaller lung volume

The Sprinter (large lung volume = large displacement) can breathe in an extremely large amount of air in a short time and run very explosively – but it also needs a lot of energy to do so.
The amateur jogger (smaller lung volume = small displacement) breathes in less air, may not run as explosively, but runs much longer and consumes less energy.

Transferred to a car, this means the following:

• A car with a large displacement is strong, fast and powerful – a lot of power but more consumption.
• A car with a small engine capacity is more economical, sufficient for everyday use and requires less fuel.

So if you now have a car with the specification 1.0 TSI, then it is a 1.0-liter engine - i.e. a displacement of 1,000 cc, although this specification is usually rounded. In concrete terms, it would usually be a number between 995 and 999 cc.

 

Calculating displacement: this is how it works

Normally, you will never have to calculate the displacement, you can find the displacement in the vehicle registration document. The formula for calculating the displacement is very complicated and requires technical understanding. For the calculation you need the number of cylinders, the piston stroke and the cylinder diameter.

The formula is as follows: π * (d/2)² * s * z

d = cylinder diameter
s = piston stroke
z = number of cylinders

We calculate the displacement using an example:

A car with 8 cylinders, each with 80 mm piston stroke and a cylinder diameter of 60 mm. The formula then looks like this: π* (60/2)²*80*8, which results in 1,800 cc, which corresponds to 1.8 liters of displacement.

Where can you find the engine capacity in the vehicle registration document?

The engine capacity must be specified in the vehicle registration document. In the registration certificate part 1, it is listed in field P.1. – this is at the right end of the penultimate row on the left side of the table. If you have an old vehicle registration document, you should find the information in field 8.

 

Long-stroke and short-stroke

In the case of cylinders, there is a distinction between long-stroke and short-stroke. Here is an explanation with examples of how these are related to displacement:

• Long-stroke:
  The piston travel (stroke) is long, the cylinder is narrow and high.
  → advantages: The engine has a lot of power even at low revs (ideal for quiet driving and economy).
  → example: Many diesel or large SUV engines.

• Short-stroke:
  The piston travel is short, the cylinder is wider and flatter.
  → advantages: The engine can reach very high revs (perfect for sporty, fast cars).
  → example: Many sports car engines.

So you can remember the following:

• Long-stroke = powerful and economical at low engine speeds.
• Short stroke = sporty and fast at high revs.

Relationship between displacement and power

In the past, it was quite easy to see the connection between displacement and performance. The larger the displacement, the more power – but nowadays this is not so easy to say, especially if a vehicle is equipped with turbochargers or hybrid engines.

 

Bigger equals better?

As already mentioned, more displacement usually equates to more power. However, we have already learned that a car with a large displacement also needs more fuel– which is no longer welcome in times of rising fuel prices and environmental aspects.

To make cars more efficient but still powerful, cars with low-displacement engines have been equipped with turbochargers, which often still have hybrid support. As a result, less fuel is consumed and the performance is still great.

Is there a trend towards smaller displacement?

In recent years, many manufacturers have developed so-called downsizing engines in order to be able to comply with the strict CO2 guidelines. In addition, the size of the engine capacity also has an impact on the calculation of vehicle tax – the more, the more expensive it becomes. Accordingly, there is still a trend towards cars with smaller displacements, but at the same time they are supposed to perform well.

Convert displacement to horsepower

When it comes to the performance of your engine, displacement is an important factor. Even with the specification of the displacement and kilowatts (kW) or horsepower (hp), it is unfortunately not quite so easy to conclude from one to the other. The conversion of displacement into hp depends on other factors such as torque, speed or medium pressure (compression of the fuel).

Without including these values, a conversion is not possible.

What is the liter output?

If you want to compare the efficiency of an engine, then the liter output is the right benchmark here. The liter output indicates how much horsepower a car has available per liter of displacement. It is important to know that large displacement does not automatically mean more liter output.

If you're thinking about it – diesel or gasoline – then you should know that cars with gasoline engines can get more horsepower out of every liter of displacement than diesel cars do. The reason: In diesel, the air content of the fuel-air mixture is larger so that soot emissions are kept low.

 

Can the displacement be increased?

If you have a car with a small displacement and want to generate more power from it, then you can have the displacement increased afterwards. This is technically feasible, but in addition to the advantages, there are also some risks that you should not ignore.

The following options are available to increase the displacement:

• To drill the cylinder: The most common method of increasing the displacement is to drill open the cylinders and thus achieve the greatest possible excess. Boring increases the displacement volume and thus also the performance.
• Crankshaft with larger stroke: When a new crankshaft with a larger stroke is installed, the injection system is adapted to fit the increased mixing demand.

Advantages of an increase in displacement

• More power: A larger displacement means that more of the fuel-air mixture can be processed, resulting in stronger combustion and therefore more power.
• Improved Torque: Better acceleration and overall handling.
• Alternative to Turbo: Without a turbocharger or compressor charger, the increase in displacement can enable an increase in performance.

Disadvantages and risks

If you want more power, then this also entails some unwanted things. Here are some risks to consider:

• Temperature: Engine can overheat faster.
• Load on engine parts: Transmission, clutch, drive shaft, tires, etc. must be able to handle the extra power.
• Exhaust gas values: More power also means that the exhaust gas values deteriorate, which can mean a higher emission class and more vehicle tax.
• Warranty and guarantee: If you increase the displacement, you will certainly lose the manufacturer's warranty and warranty.

Engine capacity and vehicle tax: An important factor

Since the displacement is a major factor for engine performance and more pollutants are emitted with more power, the displacement has been included as an important calculation factor in the motor vehicle tax. If you want to know exactly how the vehicle tax is calculated, then feel free to take a look at our guide to vehicle tax.

In addition to the engine capacity, the type of engine, emission class and first registration are also important factors that determine how high the tax is.